"It will without doubt have come to your Lordship's knowledge that a considerable change of climate, inexplicable at present to us, must have taken place in the Circumpolar Regions, by which the severity of the cold that has for centuries past enclosed the seas in the high northern latitudes in an impenetrable barrier of ice has been during the last two years, greatly abated.

(This)
affords ample proof that new sources of warmth have been opened and give us leave to hope that the Arctic Seas may at this time be more accessible than they have been for centuries past, and that discoveries may now be made in them not only interesting to the advancement of science but also to the future intercourse of mankind and the commerce of distant nations."President of the Royal Society, London, to
the Admiralty, 20th November, 1817[13]

Introduction

The `Arctic' is a general term applied to all the lands, ocean, and ice north of the Arctic Circle at 67°N. It includes the northern Canadian Archipelago, most of Greenland, the Norwegian Sea, the Arctic Ocean, and the northern coastlines of Russia, Scandinavia, Canada and Alaska.

As the above extract from 1817 shows, the
ebb and flow of Arctic ice extent and mass is nothing new, as can be
expected from such a dynamic and changing ocean/ice environment.

This is also the region which climate models indicate will receive a much larger warming from an enhanced greenhouse effect than would occur in lower latitudes. `Global Warming' is therefore not expected by
greenhouse models to be evenly distributed around the globe as the term would
suggest. Rather it is heavily biased toward the high latitude and polar
regions as clearly indicated by predictions of up to 8°C polar warming in this
map of 21st century global temperature change during the northern winter from the
Hadley (U.K.) climate model.

Fig.1 Hadley model of winter temperature change to the mid 21st century [4]

There are two good reasons for this high latitude bias in a theorised
enhanced greenhouse world.

Firstly, the infra-red (I.R.)
absorption bands of carbon dioxide lie in the 12-16 micron wavelength band.
The wavelength of strongest I.R. emission from polar ice lies in or near
this band. This means that CO2 has its greatest absorption of I.R. radiation at sub-zero
temperatures. At warmer temperatures, the typical wavelength of strongest
I.R. transmission is less than 12 microns, and therefore much less affected by CO2. At temperatures around
15°C (the average surface temperature of the
Earth), the strongest emission wavelength is around 10 microns, a wavelength
which is largely unaffected by greenhouse gases, the so-called `radiation
window' of the atmosphere where IR radiation from the surface can escape
freely to space.

Secondly, the most powerful greenhouse gas in the atmosphere is water
vapour, representing over 90 percent of the natural greenhouse effect. Water vapour shares many overlapping absorption bands with CO2 and therefore an increase or decrease in CO2 has little effect on
the overall rate of I.R. absorption in those overlapping regions. However, in the Arctic and Antarctic, the air is very dry due to the extreme cold, allowing CO2 to exert a much greater leverage in the dry atmosphere than would be possible in warmer
moister climates at lower latitudes.

It is claimed by the IPCC (Intergovernmental Panel on Climate Change)
that global temperature has risen
+0.6°C ±0.2°C during the 20th
century [6]. For this to be directly attributable to the enhanced greenhouse effect
(i.e. be human induced) that warming would have to follow the greenhouse `fingerprint', namely strong warming at the polar and sub-polar regions,
much less warming in the tropics and sub-tropics, and the least warming in equatorial
ocean regions where water vapour saturates the absorption wavebands to the point where
changes in any of the other greenhouse gases has little additional effect.

That claimed 20th century warming is based on thousands of weather stations worldwide, most of them located in cities where local heating from buildings, roads, and other structures
(the Urban Heat Island Effect) creates an artificial warming creep in the long-term data. The deficiencies in this `surface record' has been highlighted in numerous articles and papers, including
one by this author
[2].

Those deficiencies in the surface record notwithstanding, the global pattern of warming during the 20th century does not fit the classic greenhouse fingerprint. The Antarctic continent shows no overall warming since reliable records began there in
1957 as suggested by this temperature record from the South Pole itself.
Indeed, the South Pole appears to have cooled, not warmed.

Fig.2 - Annual Mean Temperature at the Amundsen-Scott Base (U.S.) at the
South Pole [9]

There has been localised warming in the 2% of the continent represented by the Antarctic Peninsula, and cooling over most of the
remaining 98%. In the Arctic, there are regions which show warming
(e.g. northern Alaska and
north-western Canada), and other regions which show
either no warming or even cooling (north-eastern Canada,
Russian Arctic, Greenland and the Arctic Rim, comparative graphs below).

Fig.3 - Annual Mean Temperature at 4 Arctic Rim stations [9]

Note: The raw data from
Svalbard (Spitzbergen) was from two separate stations during two distinct periods. They
cannot be merged together without adjustment as they had different
long-term mean temperatures. The red dotted line shows the original early data
from Svalbard. To merge them, both were compared with Danmarkshavn, and the
early Svalbard record then adjusted with a uniform correction to make the
average difference between Svalbard and Danmarkshavn equal for both periods.

Taken as a whole, there is no
significant Arctic-wide warming evident in recent decades. According to many station records there, the warmest period was around 1940, not the `warm' 1990s.

But now, a new spectre has emerged in the popular imagination - melting sea ice.

Water at the
North Pole !

In August 2000, a Russian
icebreaker, the Yamal, took a group of environmental scientists on an
excursion into the Arctic
Ocean. When they got to the North Pole they were greeted by an expanse of open
water, photographs of which became the subject of sensationalist reporting in
the media.

Among the scientists on the
cruise was Dr. James McCarthy, an oceanographer, director of the Museum of Comparative
Zoology at Harvard University and a lead author for the IPCC. "It was totally unexpected,"
he said in a report to the media. Another scientist aboard, Dr. Malcolm C.
McKenna, a paleontologist at
the American Museum of Natural History, remarked "I don't know if anybody in history ever got to 90 degrees north
to be greeted by water, not ice."

"The last time scientists can be certain the pole was awash in
water was more than 50 million years ago." proclaimed the New York Times
in an article entitled `The North Pole is melting' (August 19,
2000).

During an Arctic summer,
the sun is in the sky 24 hours per day, giving the Arctic ocean more total
sunlight than anywhere else on the planet, excepting the Antarctic during its
summer season. The result is that large areas of the Arctic Ocean are ice free
in summer at
any one time, with large leads of open water and even larger `polynyas',
stretches of open water tens of miles long and miles wide. This photo of
three submarines visiting the North Pole in May 1987 shows the whole area
criss-crossed with open water leads before the summer had even arrived.

By contrast, a similar photo taken 12 years later of USS
Hawkbill(with the ominous number SSN-666) at
the North Pole during the spring of 1999 shows a vast expanse of unbroken new
ice. (Hawkbill was nicknamed `the Devil Boat' due
to its number, and was decommissioned in 2000 shortly after its last Arctic
cruise, much to the relief of those familiar with the `Book of Revelation').

As early as 1959, the first US submarine to surface
at the North Pole, the USS Skate, did so in late March, and surfaced at 10
other locations during the same cruise, each time finding leads of open water
or very thin ice from which to do so. It did a similar cruise a year earlier
in August 1958, again finding numerous open leads within which to
surface. Here is a photo of the Skate during one of its surfacings in
1959. As can be seen in all three photos, the flat new ice is scarcely
different between 1959 and 1999, while the 1987 photo shows the extent to
which open water can occur.

An aerial view of typical sea ice shows it to be a patchwork of ice
slabs separated by areas of open water. In winter the ice will be more
continuous as the ice free areas freeze over.

Fig.7 - Aerial view of typical polar sea ice.

In the rush to sensationalise the story, the
New York Times
and other media outlets failed to check whether the
claims they were making were actually true.

For example, one crew member aboard the USS Skate which
surfaced at the North Pole in 1959 and numerous other locations during Arctic
cruises in 1958 and 1959 said: [5]

"the Skate found open water both in the summer and following winter. We surfaced near the
North Pole in the winter
through thin ice less than 2 feet thick. The ice moves from Alaska to
Iceland and the wind and tides causes open water as the ice breaks up. The Ice at the polar ice cap is an average of 6-8 feet thick, but with
the wind and tides the ice will crack and open into large polynyas (areas of
open water), these areas will refreeze over with thin ice. We had sonar equipment that would find these open or thin areas to come up
through, thus limiting any damage to the submarine. The ice would also close in and cover these areas crushing together making large ice ridges
both above and below the water. We came up through a very large opening in 1958 that was 1/2 mile
long and 200 yards wide. The wind came up and closed the opening within 2 hours.
On both trips we were able to find open water. We were not able to surface through ice thicker than 3 feet."

Other scientists and experts on the Arctic environment quickly
dismissed the McCarthy claims, pointing out that stretches of open water in summertime
are very common in the Arctic [12]. Previous Arctic explorers
even expressed
frustration at being unable to proceed over the ice due precisely to unpredictable areas of
open water obstructing their progress. The reason for the areas of open water
is that the floating ice is subject to stresses from wind, currents and tides, causing
cracking, ridging between slabs, and the creation of open leads of water
between separating ice slabs. In winter, open leads quickly freeze over from
the sub-zero air temperature, but in summer with the air temperature
often above sea water freezing point (-2°C),
such leads can remain open for extended periods.

In the end, the New York Times retracted the story. But we
should not be too quick to blame them - it was IPCC scientists aboard the Yamal, particularly James McCarthy, who first started the scare story. The
media simply took his word at face value assuming his scientific credentials
would be sufficient authority to support the story.

Recent Data on Arctic Sea
Ice

Although the `water at the North Pole' story was ultimately
discredited, there is nevertheless evidence that Arctic sea ice has recently been
thinning.

A study by Rothrock & Maykut [14] in 1999 compared upward-looking sonar data [20] from submarine cruises in the 1950s and 1960s with similar sonar data from
cruises in the 1990s. The first phase data originated with these submarine cruises.

USS
Nautilus (widebeam)

August
1958

USS
Seadragon

August
1960

USS
Seadragon, USS Skate

July
1962

USS
Queenfish

August
1970

HMS
Sovereign (widebeam)

October
1976

The second phase, was conducted between 1993 and 1997 with US submarines USS Pargo(1993) (Fig.8), USS
Pogy (1996), and USS Archerfish(1997), all of them making sweeps of the Arctic ice during the month of September.

Fig.8 - USS Pargo at the North Pole in 1993. (US Navy Photo) [17]

Since ice thickness varies according to the month of the year, the authors used a
model to adjust data from the earlier submarine cruises to normalise all
the data
to September, the month used by the later submarines. This mismatch of dates
between the various cruises introduces structural errors into the comparison
in spite of the model adjustments. The data itself did not represent ice `thickness' as such, but
`ice draft', or that portion of
the ice below sea level. Since the proportion of ice which lies above and below
the water line is well known, ice draft is a reasonable guide to ice
thickness. However, it makes no allowance for snow depth lying on the ice.

Furthermore, not all the Arctic was
analysed in this way. For
security reasons relating to the Cold War, only the `Gore Box' was involved, a
roughly rectangular region of the central Arctic which the then Vice-President
Gore moved to have de-classified for purposes of sea ice data analysis. The
criteria for determining the boundaries of the `Gore Box' is not known but it
does introduce another layer of human selectivity into the picture.

After correcting and averaging the ice draft data for the Gore Box between the two periods, the authors concluded that -

"In summary, ice draft in the 1990s is over a meter thinner than two to four decades
earlier. The mean draft has decreased from over 3 meters to under 2
meters".

A study by Wadhams and Davis [21] presented results from a British submarine cruise carried out in the Eurasian Basin in
September 1996 in which it followed a track that was close to that of the HMS Sovereign
cruise in September-October 1976. Comparing the sea-ice data from the two
cruises, they
found that mean ice draft from the
Fram Strait (the wide waterway between Greenland and Spitzbergen) to the North Pole (81-90° N and 5° E-5° W)
had declined by 43% between the two cruises. The Fram Strait is the
primary inlet for warm Atlantic water.

One problem which these various researchers
did not address was the effect of inter-annual variability on statistical
trends. This means that if the ice draft data undergoes big swings from one
year to the next, it may not be possible to establish clear trends for many
decades due to the skewing effect of the more extreme years. The Wadhams study
in particular was susceptible to this effect, since they compared two submarine
cruises in only two widely separated years. Their conclusion that there had
been a decline in sea ice draft between the two reference years could be as
much due to inter-annual variability as it was to any genuine long-term
thinning.

This problem of inter-annual variability
was however addressed by McLaren et al[7],
who analysed submarine data for the North Pole area over a 14 year period from
1977 to 1990. They found that ice draft varied up to 1 metre year
to year, while the extent of open water was subject to a variation of
2.5%. This variability in thickness is close to the figure for overall
ice thinning given by Rothrock & Maykut. McLaren et al also
determined that the data errors associated with the averaging of the ice
statistics was ±0.15 metres. To reduce errors even further, the McLaren team
chose not to use the 1950s and 1960s submarine data, but instead chose only 6
submarine cruises `on the basis of data quality and because they were
coincident in time and location'.

Sea ice researchers distinguish between
`first-year ice' and `multi-year ice', first-year ice being newly formed, typically less than 1 metre thick, and
covering the sea in extensive flat slabs. Multi-year
ice is somewhat different in that it has been subject to a long process of
grinding and breaking of slabs against each other over a period of time to
form pressure ridges many metres tall, and matching `keels' many metres deep.
Multi-year ice is distinguished by its deformed state whereas new ice is
relatively flat. According to McLaren et al,

"The
fractional coverage of multi-year ice also varies strongly on an
inter-annual basis, for example from 27.1% in 1986 to 73.8% in 1987. These
inter annual variations are sufficient to preclude definitive conclusions
about recent changes in the Arctic maritime environment."

Before accepting claims of ice thinning at face value, it must
also be
understood that the sonar equipment used in the 1990s cruises were all `narrow
beam' sonars. But the USS Nautilus and HMS Sovereign from the
earlier period used `wide
beam' sonars. To compensate for this problem corrections were made to the data from these two submarines
by multiplying all their readings by a uniform adjustment of 0.84

With narrow beam sonar, the beam is readily able to pick out keels and troughs in the underside of the
ice, so that if the ice has an undulating subsurface varying between, say, 2 metres and 4 metres, the
sonar will `see' these undulations and the computer can make a reasonable average.

This is not true of `wide beam' sonar. With a wide beam, the sonar cannot discriminate between the peaks
and troughs in the ice, and instead returns an echo which only records the thickness at the peaks, so
that any statistical averaging will come up with 4 metres (i.e. the ice thickness at the peaks) but not recording the troughs or crevices in the way a narrow beam would do. In the example just given, a
correction of 0.75 would be needed, not 0.84. If the stated beamwidth correction is inadequate,
as seems likely, the Nautilus and Sovereign data will give the impression of observing thicker ice than in fact existed at the time.
This would then compare unfavourably with the ice more accurately measured by narrow beam
sonar in the 1990s.

Apart from these reservations about the
boundaries of the Gore Box, inter-annual variability and the types of sonar used,
it is nevertheless clear that some thinning of ice draft has taken place
between the 1950s/60s and the 1990s. So, why has the Arctic ice thinned?

Fig.9 - Annual Mean Temperature at Jan Mayen [9]

Here we can see one of the longest
temperature records from the Arctic region, Jan Mayen Island 350 miles
northeast of Iceland on the fringes of the Arctic Ocean. It reveals better
than any other record that the warmest time in the Arctic was in the
1930s, not the 1990s, while the 1960s and early 70s were characterised by
anomalously cold conditions, the very period when many of the earlier
submarine cruises were made.

In other words, these latest studies claiming significant thinning
of ice between the 1960s and 1990s are comparing conditions during an
anomalously cold period with the more historically normal conditions which exist
today. Had the first phase data been collected a few decades earlier in the 1930s, it is
likely there would be little significant difference in ice thickness
between then and now.

As to why the 1960s and early 1970s should be so cold in the
Arctic, it should be noted that it was on the Russian island of Novaya Zemlya
deep in the Arctic that most of the powerful Soviet H-bomb tests were
conducted in the atmosphere during the huge Soviet test series of 1961-1962, these tests being particularly large and dirty,
the largest blast there being a mammoth 60 megatons on 30th October 1961 [11]. The cold plunge in Arctic temperatures
occurred in the immediate wake of these tests, and it took about 12
years or so for temperatures to recover to their earlier levels. It is a
strong possibility that the two events are connected.

Ice thickness is only part of the story.
There is also the question of the areal extent of sea ice. This graph shows
Arctic sea ice extent, based on satellite observation since 1973.

Fig.10 - Arctic sea ice extent 1973-1999 [10]

The total area of the Arctic Ocean is about 14 million sq. km.
The above graph shows a significant shrinkage of ice extent during 1979 at the end
of the Arctic cold period, amounting to almost 1 million sq. km., or 7% of the
total. Since 1979, the ice area has largely stabilised, reaching a brief minimum
around 1995, and increasing again since then. Put simply, the ice area
today is scarcely different to what it was in 1979. This is consistent with
observations that the Arctic atmosphere has not warmed since 1979. Had it warmed
through the 1980s and 1990s, the ice area would have
continued to shrink as increasing air temperature would have failed to re-freeze the ocean
surface.

Interestingly, during the very same period,
Antarctic sea ice increased in area by about 1.3% per decade [1], suggesting both polar regions are
responding to regional factors rather than global ones.

The fact that we have observed recent ice thinning but not
areal shrinkage of sea ice strongly suggests that the temperature of the
atmosphere (and therefore the Arctic greenhouse effect)
is not involved in the variations in sea ice thickness. A 1995
NASA study [3] also found a
possible association between the El Niño Southern Oscillation and Arctic sea
ice extent although this is not immediately obvious from either the sea ice data or the
weather station records.

Why is the ice thinner?

This might at first seem an odd question since ice obviously
melts if the temperature of the air or sea rises, thus making `Global Warming'
routinely blamed for the thinning. But this would be a premature conclusion.

Try this experiment in any kitchen -

1) Take three identical ice cubes from the
freezer compartment of the fridge
2) Place one cube in a large settled bucket of
cold tap (faucet) water
3) Place a second cube in a kitchen sieve
and let a slow trickle of cold water flow over it.
4) Place the third cube in a sieve and let
a fast
trickle of cold water flow over it.

In this experiment, the cold water from the mains water supply
is at the same temperature throughout. But which ice cube melts away the fastest?

The ice cube in the bucket will take longest to melt. The cube
under the slow trickle will melt considerably faster, while the cube under the faster
flow will melt quickest of all. And yet, the water used to achieve these three
different melting rates is at or near the same temperature.

The lesson this has for considering changes in Arctic sea ice
thickness is that there is a deep water ocean several kilometres deep directly
beneath the thin layer of surface ice. That ice can be thinned either by the
atmosphere above the ice layer, or by the ocean beneath it. In the case of the
atmosphere, the mid-summer temperature in the Arctic is barely at freezing
point, insufficient to cause such large scale thinning. There has been
little change in atmospheric temperatures in the Arctic over the last several
decades.

Here is the September temperature record for Franz Josef Land, a
Russian island deep in the Arctic only 600 miles from the North Pole,
September being the month used by the 1990s submarine cruises and the month to
which the earlier data was adjusted. The location of Franz Josef Land is
shown in Fig.12.

Fig.11 - September mean temperature at Franz Josef Land (Russia) [9]

As fig.11 shows, there has been little change in
September air temperatures since 1958, merely large year-to-year variations
which are quite normal in the polar regions. Being the record for only one month of the year,
the 1960s cold period is somewhat attenuated in this record. Since the Greenhouse Effect is a strictly
atmospheric phenomenon, and since there has been no warming, that rules out greenhouse gases
in the Arctic atmosphere as
a factor in the ice thinning.

That leaves only the ocean beneath the ice. Being liquid, its
temperature is above the freezing point of sea water, resulting in a
continuous attack upon the underside of the ice. The faster the ocean flows
beneath the ice, the faster is the melt rate, just as in the kitchen
experiment.

The observation in the submarine studies of
thinning ice cover, but with a largely constant area of ice, is consistent with changed flow rates of ocean water
beneath the ice.

Where all the Water Comes From

Here is a map of ocean currents in the
Arctic Ocean.

Fig.12 - Sources of Ocean Circulation in the Arctic Ocean [16]

As can be seen from the map, by far the greatest
contribution of surface water comes from the North Atlantic, quoted as 8 `sverdrups'. Atlantic water
flows in via the Gulf Stream which crosses the North Atlantic from the
Americas, washes the coasts of northern Europe, and proceeds up to the Arctic,
passing Jan Mayen Island and Franz Josef Land. As the water flows northward, it
slowly cools. The faster the flow, the more warmth is retained by the
water as it enters the Arctic. There is also a much smaller contribution from
the North Pacific and adjacent continental river systems, but it is the Atlantic Water
which is dominant.

Recall at this point the kitchen experiment with the ice
cubes. If the surface Atlantic water flow increases, there will be greater propensity
to melt sea ice from beneath. If the flow rate decreases, the summer ice melt rate
is less and ice can become progressively thicker with each winter. `First
year' ice tends to be thinner than `multi-year' ice and the thickness of the older
ice is largely dependent on the flows of water beneath the ice and on the
amount of ridging created through ocean movement and tides.

If the rate of flow is increased, not only will the melt rate
increase (as per the kitchen experiment), but the water itself is likely to be
slightly warmer as it enters the Arctic Ocean since it will have had less time in which to cool on its
journey north. Thus an increased flow rate is also likely to be
manifested by higher water temperature as it enters the Arctic. Results from
several submarine cruises in the Arctic during the 1990s indicate that the
influence of Atlantic water has become more widespread and intense in
the Arctic, consistent with an increased flow rate of water through the Fram
Strait and Barents Sea.

The North Atlantic
Oscillation and Thermohaline Circulation

As to why there should be changes in the rate of flow of
Atlantic water into the Arctic, it is necessary to consider what drives that
flow.

The warm Atlantic water is basically subject to a `push-pull'
action.

On the one hand, water is `pulled' into the Arctic by
Thermohaline Circulation', the tendency of surface water to get colder as it
migrates northward until it ends up colder than the deep water near the
sea bed. When that point is reached, the surface water is more dense than
the warmer deep water, resulting in the surface waters sinking.
As it does so, the bottom water is displaced, forming a slow southward moving
current along the sea floor. In this way, water entering the Arctic Ocean at
the surface is balanced by deep water leaving the Arctic in the opposite
direction.

Salinity of sea water is also a factor in
the circulation. Surface water in the Arctic Ocean is typically about 10% less
saline than the deeper water [15], which would tend to make the surface less dense
than the deeps. This is caused by injections of fresh water from continental
rivers and summer sea ice melt. Since fresh water is less dense than sea
water, it tends to cling to the surface as it spreads outwards. It is the
combined density effect of temperature and salinity between the surface and
the deeps which determines the amount of thermohaline circulation which can
occur.

Fig.13 - The start of Thermohaline Circulation

Thermohaline circulation is important for the global oceanic
balance as the water leaving the Arctic weaves its way along the sea floor,
right down the North Atlantic, into the South Atlantic, along the deeps of the
Southern Ocean, finally upwelling in the Indian and Pacific Oceans. In fig.14,
the warm surface water (red) sinks near the
Arctic and returns via a deep cold water current (brown),
resurfacing in the Indian and Pacific Oceans.

Fig.14 - Global Thermohaline Circulation

As surface
water sinks in the frigid Arctic through thermohaline action, more water is `pulled in' to fill the void
left by the sinking water.

Water is also `pushed' into the Arctic by the pressure of the
Gulf Stream, and given added impetus by the prevailing south-westerly winds that
sweep across the North Atlantic.

It is here that perhaps the biggest influence on the Arctic
sea ice manifests itself - the North Atlantic Oscillation (or NAO for short). This oscillation in the balance of
weather systems in the North Atlantic region has only recently been discovered
and is analogous to the mighty Southern Oscillation in the Pacific Ocean (El Niño / La Niña). Just as the cause and
timing of the Southern Oscillation is not yet known, the cause and
timing of the NAO is also not fully understood.

The effects of the NAO however, are all too real. The key measure of the NAO is the
`NAO Index', an
index number to indicate when the phenomenon is weak or strong. The index is
established by comparing atmospheric pressure at Akureyri in Iceland and at the
Azores.

Where the pressure gradient is shallow, the index number is
negative, and is manifested by weaker winds and storm systems in the North
Atlantic. The result is less forward forcing of the Gulf Stream by the south-westerly
winds. Where the pressure gradient is steep, the index number is
positive, and is manifested by more frequent and more intense storms, stronger
south-westerly winds, and thus more forward forcing of the Gulf Stream.

Herein lies the key to why sea ice thickness in the Arctic
might be subject to variation unrelated to atmospheric temperature. Recalling
the kitchen ice cube experiment, a stronger faster Gulf Stream driven by a
positive NAO, enters the Arctic, retaining more of its warmth due to the
faster trans-Atlantic passage of the Gulf Stream waters, and increases
the rate of summer ice melt from beneath the ice. When the NAO is negative,
the Gulf Stream is both weaker and slower, has cooled more by the time it does reach the
Arctic - and
the ice gets thicker in consequence.

Having suggested the mechanism, it merely remains to see what
the NAO state has been during recent years. The NAO is reconstructed
historically from atmospheric pressure
records from Iceland and the Azores going right back to the early 19th
century.

Fig.15 - The North Atlantic Oscillation winter index, 1825-2000 [8]

This chart shows clearly that the winter NAO was strongly positive
from 1900 to around 1930, while its most significant negative period, the time
when sea ice would be expected to increase in thickness, was during the 1960s,
the very time when the first phase of submarine sonar measurements were being taken.
Since then, the NAO has seen another strong period of positive index values,
indicative of stronger south-westerlies in the North Atlantic, and therefore
enhanced flow of warm waters into the Arctic Ocean resulting in a thinning of
sea ice.

When the NAO finally reverts to negative values, as with any
oscillatory system, the reverse will happen. Atlantic water will weaken,
become cooler as it enters the Arctic, and melt less ice than the more
aggressive positive mode of the NAO. In this way, ice thickness will vary
according to a continuing cycle.

We can see the possible effect of the NAO
in the ocean temperatures measured at the North Pole at various depths in
fig.16 [15]

Fig.16 - North Pole Ocean Temperatures at depths

As we can see from fig.16, the ocean
surface temperature in the Arctic is largely unchanged from the 1950s
through to the 1990s. Also unchanged is the deep ocean temperature.

It is only around the 250 dbar depth (a `dbar' is roughly equivalent to a metre)
that we find significant variation in ocean temperature.

The `EWG Atlas' figures originate with Soviet
surveys of the North Pole area from the 1950s to 1980s and only give
average values for whole decades. The `SCICEX' data gives values for
individual years in the 1990s and was collected by submarine cruises
on scientific expeditions. The warmest SCICEX temperatures measured at
this depth was in 1995, the coolest being in 1991.

This variability in temperature originates with
variations in the temperature of the warm Atlantic waters entering the
Arctic and is unrelated to conditions in the Arctic itself. This
variability can be achieved either through the Atlantic waters being
warmer or cooler at their source, or through the rate of flow
of those waters being changed by the NAO.

If the Atlantic water flow rate is
increased, assuming a constant rate of cooling, it will enter the Arctic Ocean
at a warmer temperature than if the flow rate is slower.

Waters at this depth cannot be warmed
directly by
the sun or greenhouse effect as solar radiation penetrates only to 100 metres
depth, while infra-red radiation from the greenhouse effect can only warm the immediate surface `skin' of the
ocean.

Fig.17 - Radiation Absorption by the Oceans at Various Wavelengths

The Sverdrup radiation chart in fig.17 shows that
solar radiation at visible wavelengths can penetrate the ocean readily,
heating it directly at depths down to 100 metres. However, it also shows
that as the radiation moves into the infra-red, the ability of the deeper
ocean to absorb heat rapidly diminishes. Once we move into the far infra red
where radiation from the greenhouse effect occurs, only the immediate
surface `skin' of the ocean can absorb that radiation. For that energy to be
absorbed down to deeper depths requires the assistance of surface turbulence
to mix in the heat. If the ocean surface is not turbulent (as
frequently happens in the tropics - the so-called `Doldrums'), energy
collected from the greenhouse effect can only warm the top millimetre of the
ocean, most of the heat being promptly lost again through evaporation.

It is for this reason that the variability
in deep water temperature in the Arctic at around 250 metres depth can only
result from variation in either the flow rate or the temperature of the
Atlantic waters entering the Arctic, the flow rate being strongly influenced
by the NAO. Atmospheric temperature changes in the Arctic itself can have no
effect on deeper ocean temperature due to this inability of water to absorb
infra red radiation beneath the ocean's surface skin or for surface turbulence
to transmit the heat down to such depths.

Conclusion

As we can see from recent history, both the
extent and thickness of Arctic sea ice is certainly subject to variation. But
it would be a mistake to assume that a brief period during which the Arctic is
in a thinning cycle is anything more than that - a cycle. We know from past
history that it has been subject to earlier retreats as suggested by the opening quote
from 1817.

Part of the problem lay in the fact that
useful data on ice extent and thickness only dates from the 1950s, yet our
temperature record from Jan Mayen Island at the edge of the Arctic shows that
the Arctic was warmer during the 1930s than it was during the 1990s.
Unfortunately there is no comprehensive ice data from the 1930s. Instead such data begins
in the late 1950s, at a time when the Arctic was entering into the grip of a known cold spell. As
that cold period ended, it is hardly surprising to find thinner ice
during the latter warmer period.

There is also the strong correlation
between the NAO and the state of Arctic ice, a strongly positive NAO in the
last decade increasing the flow rate of warm Atlantic water into the Arctic,
while it was predominantly negative during the cold period of the 1960s,
resulting in a reduced flow rate of Atlantic water and thus a reduced
propensity for ice melt.

The strong positive NAO of the last decade
is not unprecedented. While some might wish to associate this with
human-induced `climate change', it is clear from the NAO record that it was
also strongly positive during the early decades of the 20th century and even
earlier. In
other words, the NAO is a real natural cycle, not a manifestation of `global warming'.

Variability in sea ice thickness
has no implications for sea levels. Since ice sea displaces its own weight in sea
water, thickening or thinning of sea ice has a zero effect on sea level.

The freezing Arctic air which descended on North
America and Russia during the 2000 winter shows that the Arctic atmosphere has
lost none of its frigid bite, thus ensuring further renewal of sea ice.

The limits on the thickness of Arctic ice
are determined by how low the air temperature can get, and on how warm and
fast-moving the
subsurface water is. Air temperatures measured in the Arctic region show no
recent warming, thus discounting the possibility that recent thinning of ice could be
caused by atmospheric warming above the ice. Rather, the thinning of ice
in the 1990s is clearly associated with a warming of the sub-surface ocean, as
shown by the SCICEX data, caused in whole or in part by the strong NAO
increasing the flow rate of Atlantic water into the Arctic Ocean.

There is nothing in the data to suggest
anything but natural cycles at work.